Electric machines such as three-phase motors are commonly used to drive the coolant pumps in the primary loop of nuclear power plants. So that the coolant circulation can be maintained for a certain time in the event of a power failure, a flywheel is provided on the shaft on the electric machines driving the coolant pumps. These flywheels have heretofore been welded and were attached on the shaft by utilizing oil under pressure. For this purpose the wheels are provided with oil feed bores which first extend in the axial direction and are then brought in the radial direction to the seating surface of the flywheel.
Because a very high operational safety is demanded, especially for nuclear power plants, these flywheels, too, are subject to regulations which have recently been tightened substantially with respect to their manufacture and testing. The principal requirements ar now: first, the flywheels must not be welded but instead must be forged as one piece; second, the maximum stress of the flywheels must not exceed 1/3 of the yield point; and third, the wheels must permit 100 percent ultrasonic testing also for later checking.
The construction of the flywheels known heretofore and their attachment on the shaft do not meet these new requirements.